Glycine Metabolism

Abstract

Abstract Kinetic and optical properties of the pyridoxal phosphate-containing enzyme and the heat-stable, low molecular weight protein required for the exchange of bicarbonate with the glycine carboxyl group have been described. Saturation curves were determined for glycine, bicarbonate, pyridoxal phosphate, and the heat-stable protein P2; and Michaelis constants of 0.032 m, 0.031 m, 4.6 µm, and 1.3 mg per ml, respectively, were obtained. Treatment of the enzyme with cysteine removed the coenzyme and resulted in greatly decreased activity, but the activity was fully restored by incubation of the apoenzyme with pyridoxal phosphate. The ultraviolet absorption spectrum of the holoenzyme showed a maximum at 430 mµ which was reduced 85% by treatment with cysteine, but which was restored by incubation with pyridoxal phosphate. Fluorescence maxima at 390 and 500 mµ were observed when the holoenzyme was subjected to activating light at 330 and 430 mµ, respectively. The 500 mµ peak was associated with the azomethine linkage between the coenzyme and the enzyme since it was decreased by removal of pyridoxal phosphate, but the 390 mµ peak appeared to be associated only with the protein since it was not significantly altered by the above treatment.